There has been a series of reports in the scientific literature during the last decade on the corrosion protection offered by various forms of polyaniline when coated onto a metal surface that is normally prone to corrosion upon exposure to conditions which can give rise to corrosion including the following:
G. Mengoli et al., Journal of Applied Polymer Science, Vol. 26, 4247-4257 (1981) reported the anodic synthesis of polyaniline coatings onto iron sheets.
D. W. DeBerry, in Journal of the Electrochemical Society: Electrochemical Science and Technology, May 1985, pp. 1022-1026 electrochemically deposited polyaniline onto stainless steel and concluded that a polyaniline emeraldine salt coating appeared to be deposited over a native passive metal oxide film which was said to be maintained by doped polyaniline.
Los Alamos National Laboratory scientists (see ACS Polymer Preprints, Vol. 35, 265, March, 1994) have utilized a doped form of polyaniline as a primer coat with a topcoat of either epoxy or polyurethane.
Wessling and coworkers (see, for example, Adv. Mater. Vol. 6, 226, 1994) have utilized a proprietary partially doped form of polyaniline (VERSICON brand from Allied-Signal) in treating metal surfaces.
A. G. MacDiarmid and coworkers have indicated that the emeraldine state of the polyaniline had been used to coat steel which was said to be "similar" to stainless steel, which is known to persons of ordinary skill in the art to not be normally prone to corrosion, without any discussion of the results obtained in regard to corrosion protection of the metal (N. Ahmad et al., Bull. of the Amer. Phys. Soc., Program of the March 16-20, 1987 Meeting, Vol.32, No. 3, p. 548, Abstract FF10). These investigators had also earlier indicated that the p-doped (partially oxidized) form of "certain conducting polymers" had a potential suitable in principle for the anodic passivation of "certain" steels including areas from which such partially doped materials had been removed.
In another publication (NASA Conference Publication 3136, Vol. 1, "Technology 2001", The Second National Technology Transfer Conference and Exhibition, Dec. 3-5, 1991, San Jose, Calif. pp. 339-347), these authors state that "by increasing the electrical conductivity of the polymer, dopants provide the proper electronic environment to impart corrosion resistance and acid resistance to the film".
Canadian Patent Application No. 2,000,431 discloses a process for the production of thin or ultra-thin layers of inherently conductive polymers on various substrates wherein the conductive components are formed "by deposition from a meta-stable dispersion of the intrinsically conductive polymers" (page 6, lines 5-6). It is specified in this Canadian patent document that the "meta-stable dispersions are obtained when the conductive ("doped") forms of the intrinsically conductive polymers are dispersed" in particular solvents. This patent document indicates at page 7, lines 32-33 that the neutral forms of intrinsically conductive polymers "form mainly stable dispersions" so as to be distinguishable therefrom. This difference in made explicit in Examples 7 and 8 (page 16). Example 8 teaches that use of the dispersion of neutral polyaniline produced as specified in Example 7 in a "dispersion suitable for the coating process" requires dilution with another solvent "which contains the doping acid".
Recent PCT International Patent Publication No. WO 93/14166 teaches that metals can be coated with a formulation which contains polyaniline which is derived from polyaniline tosylate which has been either treated with a sulfonic acid wash to yield a partially doped polyaniline or with ammonium hydroxide to yield a so-called "neutral" polyaniline which nevertheless contains some tosylate (less than 2% tosylate per phenyl-nitrogen repeat). This PCT patent reference illustrates the use of polyaniline coatings containing other ingredients, such as dispersing liquids, binders, pigments, and the like, rather than a neat polyaniline coating.